1. Technical Field of the Invention
The present invention relates to an image processing apparatus which is able to recognize an object on acquired images by extracting change points of signal levels, based on the signals inputted from an on-vehicle camera which is provided with solid-state image acquisition elements.
2. Related Art
Lane control systems that have been known include one which performs a white line recognition process. In the white line recognition process, white line portions are extracted (recognized) from an image of the road surface in the forward direction of the vehicle, which image is acquired by an on-vehicle camera (hereinafter referred to as an “acquired image”). With this process, the position of each white line with respect to the vehicle is estimated. When it is determined that the vehicle has a high possibility of deviating from the traveling lane, on the basis of the positions of the white lines and the behaviors of the vehicle, the driver is warned or traveling control is effected to keep the lane.
On-vehicle cameras in general are represented by such image acquiring devices as CCD (charge-coupled device) imaging sensors and CMOS (complementary metal oxide semiconductor) imaging sensors. Such an imaging device is adapted to photoelectrically convert an optical subject image, which is imaged via a lens, into electric charges using a plurality of solid-state image acquisition elements (hereinafter just referred to as “image acquisition elements”) arrayed on a substrate. Then, the output voltage of the image acquisition elements are adapted to be read out in the scanning direction and the read-out signals (hereinafter referred to as “luminance signals”) are adapted to be outputted to a control apparatus.
The white line recognition process is performed, as shown in FIG. 4A, based on the luminance signals inputted from the on-vehicle camera. Here, the points where the signal levels of the luminance signals change with level differences equal to or more than a predetermined threshold, are referred to as pixel points (edges) P. Further, of the regions each sandwiched by two adjacent edges P, the regions on the side where the levels of the luminance signals are high are referred to as regions H. In the white line recognition process, the pixel points P are extracted for every horizontal line in an acquired image X, and the pixel points P that belong to the regions H are set as white line candidate points. Then, the position of each white line is estimated based on the linkage between the white line candidate points in the entire acquired image. Reference may be made to Japanese Patent Application Laid-Open Publication No. 2000-242800, for example.